The invention is based on a method for the injection of fuel and fuel injection apparatus for performing the method. In a method of this kind known from German Offenlegungsschrift No. 26 36 659, the combustion chamber of each cylinder of the internal combustion engine to be supplied with fuel is subdivided into a secondary and a primary combustion chamber, the two being connected via a straight channel. In this engine with externally supplied ignition, the fuel is introduced via an injection valve in such a manner that a portion of the injected fuel travels via the straight channel and reaches the secondary combustion chamber, while another portion of the fuel is injected directly into the primary combustion chamber. The apportioning of the fuel quantity to be injected to the primary combustion chamber and the secondary combustion chamber is varied in accordance with load such that a readily ignitable and stoichiometric fuel-air mixture is always formed in the secondary combustion chamber. The purpose of the layered combustion process thus realized is to introduce a relatively lean fuel-air mixture into the primary combustion chamber, so that toxic substances forming during combustion in the primary combustion chamber, predominantly because of the flame-extinguishing effect at the combustion chamber walls and in niches in the combustion chamber can be held to a minimum. If a fuel-rich mixture is located in combustion chamber niches in the vicinity of the combustion chamber walls, then the proportion of the fuel components no longer being combusted completely is greater than if a fuel-poor mixture or if only air is located in such regions. The inflammation of the relatively lean fuel-air mixture in the combustion chamber is enabled by means of a torch ignition means. The igniting torch is the product of the mixture, which has been inflamed in the secondary combustion chamber by means of the spark plug, as it flows out of the connecting channel toward the primary combustion chamber. For a homogeneous mixture formation, in particular in the secondary chamber, the injection of the fuel takes place relatively early, and the end of injection should occur approximately 90.degree. to 120.degree. before top dead center. Especially in the upper load range, however, the injection onset may be retarded until during the beginning of the intake phase, so that a large amount of time is available for mixture formation.
This known apparatus is very expensive, however, because of the necessity for a secondary chamber and the specialized fuel injection nozzle. Furthermore the known apparatus relates to a combustion method which operates with highly fissured combustion chambers, which in comparison with an internal combustion engine having a simple combustion chamber is associated in principle with less advantageous fuel consumption. Internal combustion engines having specialized, externally supplied ignition and direct injection into a simple combustion chamber have substantial advantages in terms of fuel consumption. However, they do have the disadvantage that despite external ignition the maximum output theoretically possible with this engine construction cannot be realized, because the injection causes the premature occurrence of elevated soot emission levels, similarly to what may happen in self-ignited engines under full-load operation. This soot emission can be ascribed to the incomplete combustion of the fuel, which could not be prepared well enough in the time between the instant of injection and the instant of inflammation.
From SAE Paper No. 78 0699, an internal combustion engine is known in which the fuel is injected directly into a simple combustion chamber, and the mixture thereby formed is ignited with the aid of two spark plugs and the compression ratio increased to 11:1. Fuel injection in an engine of this kind is controlled such that at low load the fuel is introduced into the vicinity of the spark plug immediately prior to the instant of ignition, so that an ignitable mixture is produced there, despite the low fuel injection quantity relative to the total air charge of the combustion chamber. With increasing load, the instant of injection is shifted toward "early", so that at maximum load the injection is terminated at 70.degree. to 90.degree. prior to top dead center. In this engine, specialized additional provisions are made for fuel preparation; in detail, these are inducing turbulence in the air entering the combustion chamber, a high exhaust gas recirculation rate and a high compression ratio. These provisions again occasion considerable expense, which it would be desirable to reduce. Furthermore only a small crankshaft angle range, and a decreasing period of time as the engine speed increases, are available for mixing the fuel thoroughly with combustion air.